Object-Oriented Programming: Polymorphism and Interfaces - Java: How to Program Early Objects - page 409

implement earnings , class SalariedEmployee must be declared abstract —otherwise,
class SalariedEmployee will not compile. Of course, we want SalariedEmployee to be a
concrete class in this example.
Method toString (lines 45-50) overrides Employee method toString . If class Sala-
riedEmployee did not override toString , SalariedEmployee would have inherited the
Employee version of toString . In that case, SalariedEmployee 's toString method would
simply return the employee's full name and social security number, which does not ade-
quately represent a SalariedEmployee . To produce a complete String representation of a
SalariedEmployee , the subclass's toString method returns "salaried employee: " fol-
lowed by the superclass Employee -specific information (i.e., first name, last name and social
security number) obtained by invoking the superclass's toString method (line 49)—this is a
nice example of code reuse . The String representation of a SalariedEmployee also contains
the employee's weekly salary obtained by invoking the class's getWeeklySalary method.

10.5.3 Concrete Subclass HourlyEmployee
Class HourlyEmployee (Fig. 10.6) also extends Employee (line 4). The class includes a con-
structor (lines 10-25) that receives a first name, a last name, a social security number, an
hourly wage and the number of hours worked. Lines 28-35 and 44-51 declare set methods
that assign new values to instance variables wage and hours , respectively. Method setWage
(lines 28-35) ensures that wage is nonnegative , and method setHours (lines 44-51) ensures
that the value of hours is between 0 and 168 (the total number of hours in a week) inclusive.
Class HourlyEmployee also includes get methods (lines 38-41 and 54-57) to return the val-
ues of wage and hours , respectively; a method earnings (lines 60-67) to calculate an Hour-
lyEmployee 's earnings; and a method toString (lines 70-76), which returns a String
containing the employee's type ( "hourly employee: " ) and the employee-specific informa-
tion. The HourlyEmployee constructor, like the SalariedEmployee constructor, passes the
first name, last name and social security number to the superclass Employee constructor
(line 13) to initialize the private instance variables. In addition, method toString calls su-
perclass method toString (line 74) to obtain the Employee -specific information (i.e., first
name, last name and social security number)—this is another nice example of code reuse .

1 // Fig. 10.6: HourlyEmployee.java

2 // HourlyEmployee class extends Employee.

3
4 public class HourlyEmployee extends Employee

5 {

6 private double wage; // wage per hour

7 private double hours; // hours worked for week

8
9 // constructor

10 public HourlyEmployee(String firstName, String lastName,

11 String socialSecurityNumber, double wage, double hours)

12 {

13 super (firstName, lastName, socialSecurityNumber);

14

Fig. 10.6 | HourlyEmployee class extends Employee . (Part 1 of 3.)